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Old 05-05-2019, 06:54 PM   #1
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V10 RPM Limit

A question for the Ford people who are/were deep into the programing of the ECU.

We all have read the occasional posting concerning the high RPM on a hill descent and we all tell the owner not to worry the engine is made for high RPM. But I'm wondering about something with this scenario. I know the the RPM limiter of the V10 won't let me past around 5250 RPM with my right foot or that I can't go much faster than 3000 RPM in top gear, at least that's what I've experienced. But what happens on a downhill run if I manually downshift to a low gear and let the speed of the coach go to where ever? The limiter will have no effect considering the engine is at idle. Will the ECU force an upshift and override my manual selection? I don't think the programers would include a shut down as the engine will for an over heat. Loss of the power assisted brakes and steering would not be good in this situation. What's to stop an overspeed other than operator action?

Granted any reasonable operator would let the situation get to this point and the 5250 limit with the throttle is probably conservative by a few thousand but human nature being what it is,,,,
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Old 05-06-2019, 05:03 AM   #2
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rpm

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Originally Posted by Sweetbriar View Post
A question for the Ford people who are/were deep into the programing of the ECU.

We all have read the occasional posting concerning the high RPM on a hill descent and we all tell the owner not to worry the engine is made for high RPM. But I'm wondering about something with this scenario. I know the the RPM limiter of the V10 won't let me past around 5250 RPM with my right foot or that I can't go much faster than 3000 RPM in top gear, at least that's what I've experienced. But what happens on a downhill run if I manually downshift to a low gear and let the speed of the coach go to where ever? The limiter will have no effect considering the engine is at idle. Will the ECU force an upshift and override my manual selection? I don't think the programers would include a shut down as the engine will for an over heat. Loss of the power assisted brakes and steering would not be good in this situation. What's to stop an overspeed other than operator action?

Granted any reasonable operator would let the situation get to this point and the 5250 limit with the throttle is probably conservative by a few thousand but human nature being what it is,,,,

I have read that iit will upshift while going downhill if rpm exceeds 5250 rpm
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Old 05-06-2019, 03:56 PM   #3
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5,250 RPM if it is not in gear and flat footed, 5,550 to 5,600 RPM if in gear under power. If you have "Tow/Haul" and are have it engaged, it may up-shift. May depend on the year and if the ECU has the latest profile or not. I do not have the tow/haul feature and it has been to 6,000 and a little higher in 2nd gear and coasting down grade. Brakes are needed on steep down hills.
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Old 05-06-2019, 07:44 PM   #4
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My suspension is it will up shift even with a manually selected gear. Been a long time since shift linkage directly control clutch solenoids so all it needs is a line of code.

I did the math for my 2006 chassis with a five speed and in second gear it will hit 6K RPM at around 50 MPH so it's possible to get there. I've been meaning to call 5 Star Tuning with a separate question maybe I ask them.
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Old 05-16-2019, 12:23 PM   #5
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I have never had that experience. Go up and down 6-7% grades all the time. Use Tow/Haul. Average 4200, have occasionally seen 4700, never seen over 5k.

Going down same thing. Do not let speed exceed 45 going down 6-7% grade. Will use the brakes as required with Tow/Haul.
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Old 05-17-2019, 11:33 AM   #6
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But what happens on a downhill run if I manually downshift to a low gear and let the speed of the coach go to where ever?
It will force an upshift.

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Originally Posted by Sweetbriar View Post
The limiter will have no effect considering the engine is at idle. Will the ECU force an upshift and override my manual selection? I don't think the programers would include a shut down as the engine will for an over heat.
Sure it will include a shut down. When the engine is providing braking force most of the time the fuel is completely turned off. There is zero fuel being injected into the engine. The transmission is keeping the engine turning.
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